The engine idles fine when started, barring the occasional stall initially. Engine pulls great, feels smooth when applying & releasing throttle. Economy 32mpg (UK) about town, 38mpg on motorway, which I reckon is pretty good. Stopping at lights, the idle is around 800 revs, a bit lumpy but basically ok. Temp is about 1/3 up the guage, or 1/4 on motorway.
After driving for a 'while' (anything from 5 mins to 30 mins) the engine mode will change - applying or releasing the throttle makes the engine jerk, and when stopping at lights, the idle will bounce between
1000 & 1100 revs, once a second. These two symptoms are always concurrent. The economy is the same as before. This switch in modes seems unrelated to time, or temperature. It often follows a sprint of heavy throttle / acceleration. The engine will stay in this mode until it's shut off. when restarted, the first (smooth) mode occurs, and the cycle repeats.
I've changed the ISV, without major difference. I also found and repaired a bad vacuum hose, which helped the 'good' idle a bit, but didn't change the second 'bad' engine mode.
Any ideas on where I should look next?
Many thanks, Jamie
Any ideas on where I should look next?